Air inducted into an engine during idle can be regulated in several different ways. For example, an auxiliary air throttling valve may be connected in parallel with a main throttling valve. When the main throttling valve is closed, the valve position of the auxiliary valve can be used to regulate the air amount inducted into an engine. In addition, an engine air amount may be regulated during idle via an electronic throttle. By using an electrical actuator to control valve position of a single throttle, the engine air amount during idle may be controlled. Furthermore, electromechanical intake valves can also regulate engine air amounts inducted during idle. By controlling the intake valve opening and closing positions (and/or lift amount), engine inducted air amounts may be controlled. The above illustrate various idle air amount throttling valves.
Because each of the above mentioned valves can be automatically controlled, i.e., controlled at least in part by an electromechanical control system, it can be beneficial to determine when degradation of the idle air regulating device may have occurred.
One method to determine degradation of an auxiliary idle air control valve is described in U.S. Pat. No. 4,875,456. This method presents a means to determine valve degradation of an auxiliary air control valve used to bypass a main throttle valve of an intake air system. The method compares an air amount detected in a main air intake passage to an air amount calculated from the valve position of an auxiliary air control valve while the main throttle is closed. If the air amount detected in the main air intake passage is greater than the air amount calculated from a valve position of the auxiliary valve by a predetermined amount, valve degradation is determined.
The above-mentioned method can have several disadvantages. For example, the approach determines valve degradation is present if a determined amount of air is inducted into an engine is greater than an air amount determined by valve position. In other words, if less air flows into an engine than desired, valve degradation is not determined. In addition, the method may not be beneficial in determining if an engine is warming up as desired. For example, during a cold start, engine idle speed can be elevated to reduce the time to warmed-up engine operation. If less air is flowing into an engine than desired, engine speed may be reduced, thereby increasing the amount of time to a warmed-up condition. This may increase engine emissions because emissions can be lower in a warmed-up engine.
Another method to determine degradation of an auxiliary idle air control valve is described in U.S. Pat. No. 5,408,871. This method presents another approach for determining valve degradation of an auxiliary air control valve used to bypass a main throttle valve of an intake air system. The approach appears to rely on an engine speed check and a spark check to enable the valve diagnostics. Further, the method appears not to enable the diagnostic until certain criteria are met, such as engine coolant temperature.
The above-mentioned method can also have several disadvantages. For example, if the diagnostic is not enabled until after the engine is warmed up, degraded valve performance that may occur during cold starting conditions may not be identified. This can lead to cold starting operation where less airflow is provided than desired, resulting in slower catalyst warm-up and therefore increased emissions.
The inventors herein have recognized the above-mentioned disadvantages and have developed a method of determining degradation of an idle air throttling valve that offers substantial improvements over prior methods.